Depending on the materials they are made of, noise barriers can have very different sound absorbing or sound redirecting characteristics. By way of example, noise barriers made of autoclaved aerated concrete (better known with the “porenbeton” trade name), although presenting many technical advantages, generally have quite poor sound absorbing performances. In fact, it is known that such barriers, when not processed with special treatments, fall within the A1 classification (the lowest one according to UNI EN 1793-1 Regulation) while, depending on the practical applications, it should be necessary to cover all acoustic classifications until the highest one, e.g. A4.
Such a problem is of course present not only with barriers made of porenbeton, but also with those made of different materials such as, for example, normal concrete.
For this purpose, the present applicant has filed, on Feb. 13, 2009, an Italian patent application (No. PI2009A000013) disclosing a plurality of sound absorbing acoustic boxes which can be applied to a sound redirecting barrier in such a way to locally increase its sound absorption characteristics, to optimize the absorption of sound by the barrier according to the needs and find the best balance between the intrinsic sound redirecting properties of the barrier and the sound absorption.
According to the above patent application, the boxes have a parallelepiped shape and are filled with a proper sound absorbing material. The front side of the boxes is then perforated so that the sound captured by the boxes enters the boxes themselves to be then absorbed by the sound absorbing filling material.
However, such acoustic boxes are not particularly efficient insomuch as a large number of them needs to be applied to increase the sound absorption properties of the barrier until reaching A4 level, with a consequent increase in costs and difficulties in the production, assembly and maintenance.